Considering how rare Antimatter is in our predominately 'matter' dominated universe I cannot see how one would form.In the event of a collision there would no doubt be a large burst of .551Mev radiation.It has always been assumed that Gravity does not care whether it is matter or antimatter but I don't know whether this has been verified by experiment yet.

My counter-suggestion was that maybe 1 of these was an anti-matter BH which was smaller than the matter BH; in which case all, or at least most, of the anti-matter would disappear and predominantly matter would be left.

Do you think there is any chance that matter/energy could somehow escape from such a scenario? Or could the event horizon be pushed so far away that our universe could be existing within it? Maybe, even, our universe surrounds a naked SMBH?

This sort of thing is way beyond the limit of my knowledge of the subject, but I do have a fertile imagination []

I can well imagine that we are living inside a SMBH but the problem arises where is the singularity ? should we not be orbiting around it or falling towards it ?.I have heard talk of a 'Great attractor' and a 600 Km/sec movement relative to CMBR but do not know if this is current thinking.

We may well be orbiting the singularity; but, as everything is rotating, nothing is rotating relative to anything else so we wouldn't know as there is nothing to measure the rotation against (George may have something to say about angular momentum here).

As for where the singularity is, I've never been comfortable with the point of view that there is no centre to the universe. Yes, everything is moving away from everything else (on the largest scales) due to the expansion of space; but if the universe expanded from a point then that is where the centre would be. Were it possible to draw lines from 1 side of the universe to the other in the x, y and z axes, then where they intersect is the centre.

The Great Attractor:

from http://csep10.phys.utk.edu/astr162/lect/gclusters/attractor.htmlCalculations indicate that ~1016 solar masses concentrated 65 Mpc away in the direction of Centaurus would account for this. This mass concentration has been dubbed the Great Attractor. Detailed investigation of that region of the sky (see adjacent image of the galaxy cluster Abell 3627) finds 10 times too little visible matter to account for this flow, again implying a dominant gravitational role for unseen or dark matter. Thus, the Great Attractor is certainly there (because we see its gravitational influence), but the major portion of the mass that must be there cannot be seen in our telescopes.

The “Great Attractor” is a distant, mysterious entity that seems to be tugging tens of thousands of galaxies, including ours, rapidly toward itself.

The new findings suggest these motions are the result of gravitational forces from not one, but two things: the wall, and a conglomerate of galaxies far beyond it.

It seems “roughly 50% of our galaxies’ motion through space is due to [the wall] and about 50% is due to structures behind it,” wrote Dale Kocevski of the University of Hawaii in an email. Kocevski is a member of one of the research teams that reported the findings.

Astronomers have known for years that something seems to be pulling our Milky Way and other galaxies toward itself at a breakneck 22 million kilometers (14 million miles) per hour.

But they couldn’t before now pinpoint exactly what or where it is.

Although it’s tugging on us, we’ll never reach it, said David Radburn-Smith the University of Durham, U.K., whose team identified the “wall.” That’s because the expansion of the universe is stretching the wall’s neighborhood away from ours about nine times faster than the speed with which gravity is drawing them together. The stretching effect would be still swifter for further objects.

Radburn-Smith and colleagues described the “wall” in a new paper accepted for publication in the research journal Monthly Notices of the Royal Astronomical Society. It “does appear to be a wall-like slab of galaxies,” he wrote in an email, though its precise shape is “tricky to define” because the dust of our Milky Way galaxy obscures much of it.

Radburn-Smith, a Ph.D. student, is the paper’s lead author.

He added that the wall contains the weight equivalent of some 12,000 Milky Way galaxies, and is around 200 million light-years away. A light-year is the distance light travels in a year.

The wall seems to sweep over an angle of about 100 degrees near the top of the Southern Hemisphere sky, the astronomers wrote; this distance corresponds to some 400 million light-years. One end would be roughly in the direction the star Mu Velorum in the constellation Vela, the other in the vicinity of Al Dhanab in the constellation Grus.

In between, the structure curves into the silvery strip of the Milky Way, they reported, where it merges with a cluster of galaxies called Norma—roughly in the direction of the star Beta Trianguli Australis in the Southern Triangle constellation. One member of the team, Patrick Woudt of the 3University of Cape Town, South Africa, proposed previously that Norma marks the core concentration of the Great Attractor’s mass.

The researchers drew their results from an array of galactic distance measurements based on redshift—the reddening of light from galaxies. Further-off galaxies are redder because as the universe expands, it pulls objects apart from each other, “stretching” light waves traveling between them. The greater the distance between objects, the stronger the effect.

Surveys of the universe at its largest scales have found that galaxies are arranged into a sponge-like structure, with sheets and filaments of galaxies surrounding nearly empty voids. Places where these sheets and filaments intersect are sometimes called “knots,” as they tend to have dense concentrations of galaxies that are merging.

Radburn-Smith said his findings help clarify our place in this sort of structure.

The Milky Way and its neighboring Andromeda galaxy, along with some 30 smaller ones, “form what is known as the Local Group,” he explained in an email. This lies on the outskirts of a “supercluster”—a grouping of thousands of galaxies—known as Virgo, which is also pulled toward the Great Attractor.

The Virgo Supercluster is centered on a “knot,” he added. The Local Group lies on a broad filament protruding from this knot. Another filament also branches off from it—at right angles to ours—and extends to a second knot, known as the Centaurus cluster, he added.

From there, yet another filament stretches toward a third knot, the “Norma Cluster,” which is part of the Great Attractor wall, he explained. “There’s no direct connection between our galaxy and the Great Attractor.”

Astronomers have previously found other sheet-like conglomerations of galaxies described as “Great Walls.” This newfound structure may be similar, Radburn-Smith suggested.

But Kocevski said his own work shows the wall and associated structures lack enough mass to provide the gravitational pull hitherto attributed to the Great Attractor. Thus, he proposes that more mass lies beyond the wall.

In findings presented Jan. 11 at the American Astronomical Society meeting in Washington, D.C., Kocevski, also a doctoral student, and other researchers at his institution said a major concentration of galaxies lies beyond the Great Attractor. They’re near the so-called Shapley Supercluster, 500 million light-years away—the most massive known supercluster.

Kocevski wrote in an email that his and Radburn-Smith’s findings could both be correct; in fact, “our work mapping X-ray luminous galaxy clusters in the Great Attractor region has reached the same conclusion” as Radburn-Smith. “The pull our galaxy is feeling is most likely due to both the nearby Great Attractor and these more distant structures.”

The researchers are using the name “Great Attractor” only for the wall and related structures, not these much further objects. The naming is in line with past practice: astronomers had long suspected the Great Attractor lay in the neighborhood now being fingered as the abode of the wall. Thus they called that zone, but not the area behind it, the “Great Attractor region.”

This article has been corrected since its initial posting: The Great Attractor is believed to be pulling tens of thousands of galaxies toward itself, not millions as originally stated.

A black hole could be predominantly antimatter and it would be identical to an ordinary black hole and assuming that there was no matter orbiting the holes the collision between the two would produce nothing other than a big burst of gravitational wave radiation.

What happens inside the event horizon is another matter but however violent that was we would see nothing of it.

Ian - the matter & anti-matter would annihilate each other. Wouldn't that mean the mass, and hence the gravitational attraction, would decrease? If so, could it decrease to the point where there is insufficient mass to maintain itself as a BH?

I don't know enough about the physics of matter & anti-matter colliding except that I was under the impression that they would totally annihilate each other in a massive burst of energy (100% conversion of matter to energy - or close to). Also, I believe that gravitational waves are being sought but have not been found thus far.

If a star collapses into a blackhole does it matter whether or not it was a matter or anti matter star surely the resulting blackhole would be identical in either case. there can be no such thing as an anti matter blackhole

That is an equally valid argument until we have a good model as to what is going on inside a black hole.

Unfortunately no one seems to be working on this because they all say "we don't understand the final state of the gravitational collapse without a theory of everything including quantum gravitation. That may be so but immediately after the black hole forms the initial stages of the collapse are quite understandable using current classical and quantum physics so the early stages of the process can be modelled exactly.

Syhprum - Surely, any atoms that fall into a BH would be broken into their constituent parts, then those parts broken down into fundamental particles such as electrons & quarks. Were the BH made from anti-matter, those particles would be positrons and anti-quarks.

If, however, those particles are subsequently converted to energy, wouldn't both a matter BH and an anti-matter BH end up with more-or-less neutral charge? If that is the case, then what you say is correct. (or can you get anti-energy?)